In lighting devices of the relevant type which are present as white-emitting LED lamps, a blue light emitted by light-emitting diodes (LEDs) is at least partly converted into yellow light in the phosphor region. In total, a blue-yellow or white mixed light is thus emitted by the phosphor region. The phosphor region appears yellow when viewed from outside with an LED lamp switched off. This yellow appearance is intended to be avoided, however, in many applications.
LED lamps are known in which the phosphor region is covered by a diffusely scattering bulb. As a result, the yellow phosphor region shows only slightly through the bulb. In this case, the phosphor cannot be arranged on the exterior of the outer bulb, since the yellow impression is then too strong. Internal phosphor is thermally disadvantageous, however, since it is not cooled by ambient air.
Conventional incandescent lamps of the DIADEM type from Osram are known for use as indicator luminaries in automotive engineering, said lamps having a blue filter on their bulb. By means of the blue filter, the blue component is filtered out from the wide optical spectrum of the incandescent lamp (that is to say is reflected back into the lamp), such that only yellow or yellowish light emerges.